You do not even have to use a playlist - just ***** all the cards of the model you want to the "next" entry in the "now playing" tab.
The easiest way to select all the cards for one model is via the "My Collection" tab. Enter the model's name in the search box, use control-A to select all cards and then ***** them to the now playing tab.
It would be nice if you could select multiple cards from the girls details "other cards" tab, but it only allows you to ***** them one at a time from there.